The present invention relates generally to position or orientation sensors, and more particularly to orientation sensors used to provide input to a computer system, manipulate a virtual reality environment in a computer, and control sensory impressions conveyed to the user of the computer.
There are various input devices known for controlling a computer in response to the orientation of a body part of a user. The most common in use is the conventional "mouse" device, in the form of a hand-sized housing which is moved over a flat desktop. Motion over the desktop is sensed by means of a mechanically rotating ball or optically reflective sensor, and the digital data which is generated translates into a corresponding orientation signal which determines the location of the user's hand and is input to the computer. Other positioning devices include the graphics input tablet, consisting of a flat sensor pad and a hand-held pointing stylus, which translates the analog motion of the pointing stylus into digitized data. Still other devices rely on focused light sources, held by the user or fixed on the user's person, as on a pilot's helmet. As the user aims the light beam, sensors mounted around a display screen track the movement of the beam and translate this movement into a corresponding orientation signal to input into the computer.
Devices such as those discussed above are basically effective, although they suffer from certain disadvantages. Most input devices require a fixed, generally level surface upon which to operate, or must operate in conjunction with a stationary sensor of some type; that is, motion is sensed with respect to a fixed medium and positional data signals are generated and presented to a computer for translation into a corresponding orientation signal. The need for a fixed surface or stationary sensor constrains how the user may interact with the display device. The user must normally sit close to a display screen and be provided with ample level desk space for placement of the graphics tablet or movement of the "mouse." In the case of the stationary sensor, the user must confine movement to keep the light beam within range of the sensor array and aimed appropriately. These sensors which depend on the sensing with respect to some fixed object are source-dependent. It is desirable to use a sourceless sensor, that is a sensor which does not depend on the existence of some external fixed object which is used to determine the orientation of the sensor.
In U.S. Pat. No. 5,068,645 (Drumm) a sourceless orientation sensor operates on the principle of refracted light beams. The orientation sensor includes a hollow spherical housing containing a gaseous medium and a gaseous medium, each with a different index of refraction and each filling the housing to the one-half level. The sensor uses light source-photodetector pairs. The light source in the form of an LED and photodetector of each pair are mounted on opposite sides of the spherical housing. As the housing is rotated, the angle of incidence of the focused light beam from the LED on the boundary layer changes, causing the refraction angle and therefore the light intensity on the photodetector to change. A pair of coplanar light sources and photodetectors are located 45.degree. from the horizontal plane. The output voltage for the photodetectors are compared, and the resultant output indicates the direction and magnitude of tilt. With two pairs of opposing light sources and photodetectors, the direction and magnitude of tilt in two axes can be determined.
The orientation sensor of U.S. Pat. No. 5,068,645 suffers several drawbacks. First, the sensor is only capable of measuring the tilt of the housing away from the vertical axis, it cannot measure any azimuthal rotation. Second, the sensor has an effective range of tilt of only about 30.degree.. Third, the sensor suffers from a "sloshing effect", in that when the housing is suddenly tilted, the liquid medium flows back and forth creating surface waves on the boundary surface. The uneven boundary surface refracts light differently and creates errors in the measured tilt angle.
The present invention overcomes the disadvantages of the prior art devices, such as the requirements of flat desktop or aiming of a light source, the inability to measure azimuthal angle, the limited range of tilt angle, and the "sloshing effect".
In accordance with the present invention, a novel input device is provided for an electronic device. The input device includes a sourceless orientation sensor which generates an electrical signal representative of the physical orientation of the device, without it being adjacent to any fixed reference object. The electrical orientation signal can be used to position and otherwise control a cursor on a display screen, to manipulate virtual objects in a virtual reality environment, to control the presentation of an image on a display screen, to send orientation information to storage, or to provide feedback for a robotic device.
The input device is in the form of a frame with an azimuthal orientation sensor and a tilt orientation sensor attached. The azimuthal sensor detects the magnitude of rotation of the frame about the vertical axis, and the tilt sensor detects the magnitude and direction of tilt of the frame away from the vertical axis. Thus complete information on the pitch, roll, and yaw of the frame is available.
The frame can be temporarily affixed to a body part of the user. In a preferred embodiment, the input device is a headset to be worn by a user. Wearing the device, the orientation information corresponding to head movements is input to the computer to change the display on a display screen.
The azimuthal orientation sensor operates on the principle of comparing the orientation of the sensor to the local magnetic field generated by a planet, and using the difference to determine an azimuthal angle. In the preferred embodiment the azimuthal orientation sensor includes a flux gate magnetometer and associated electronics to drive the magnetometer and detect signals from the magnetometer. The magnetometer includes a saturable core, and by driving the core to near its magnetic saturation, any additional local magnetic field causes flux to leak from the core. Two detection coils at right angles detect the flux leakage and thereby sense the direction of local magnetic field. As the azimuthal orientation sensor is rotated, the signals from the detection coils change.
It should be noted that as the sensor is tilted relative to the vertical, the projection of the core of the magnetometer onto a plane perpendicular to the magnetic field changes. Therefore the output from the azimuthal sensor output must be corrected for the tilt angle by a calculation of the aforementioned projection area. In the preferred embodiment this correction is implemented in hardware. Alternatively, the correction may be implemented in software by for instance generating a table of tilt angle versus projection area of the core. Another solution to this problem is to use an array of three magnetometers aligned along mutually perpendicular axes, whereby the magnetic field is generated as the vector sum of the three magnetometer outputs and the azimuthal angle of the magnetic field is easily determined.
The tilt orientation sensor operates on the principle of a light beam being refracted as it passes from one transparent medium to another. The orientation sensor includes a hollow spherical chamber disposed inside an opaque enclosure. The transparent chamber has a defined central axis passing through its center point. Contained within the chamber are two fluid media. The first medium is gaseous and the second medium is liquid, and each has a predetermined viscosity and a different index of refraction. The liquid medium fills the chamber to the one-half level and the boundary between the liquid and gas intersects the center point of the chamber. The liquid medium always flows to the bottom half of the spherical housing to maintain equilibrium.
A light source in the form of an LED is mounted next to the chamber in the housing to shine its maximum intensity along the central axis. A plurality of photodetectors in the form of phototransistors are mounted next to the chamber but spaced apart from the central axis. The light source emits a focused beam and the photodetectors receive the focused beam and generate an analog voltage representative of the intensity of the received beam.
When the focused beam emitted from the light source passes through the boundary between the gaseous and liquid media, refraction of the beam occurs at the boundary at an angle which is determined by the angle at which the incident light beam intersects the boundary. If the chamber is oriented so that the central axis of the incident light beam is perpendicular to the boundary, the light beam will not be refracted at all. If the photodetectors are spaced equally apart from the central axis, they will receive equal intensities of the light beam, and will generate equal signals. As the chamber is rotated with respect to the vertical axis, the angle from the vertical axis to the incident light beam will increase, and the refraction angle of the light beam will increase. As the refraction angle increases, the axis of maximum illumination will move toward one or the other of the photodetectors. Therefore, one photodetector receives a decreasing light intensity beam and generates a decreasing voltage while and another photodetector receives an increasing light intensity and generates an increasing voltage. The difference between the output voltage of the photodetectors is therefore representative of the angle at which the incident beam intersects the boundary between the two media.
In a preferred embodiment of the present invention, the tilt orientation sensor includes a light source and four photodetectors. Two photodetectors are located in one vertical plane which includes the central axis, and the other two photodetectors are located in a perpendicular vertical plane. The light source is mounted on the one side of the housing and the photodetectors are mounted on the opposite side. In the normal orientation of the sensor, the light source is located in the upper half of the spherical housing, near to the gaseous media. The photodetectors are located in the lower part of the spherical housing, near to the liquid media, each 64 degrees from the horizontal axis. The output voltages for each pair of photodetectors within the same plane are compared in a differential amplifier, and the resultant output of the differential amplifier indicates the direction of rotation as well as the magnitude.
Also in accordance with the present invention, a transparent rigid disk is placed inside the chamber. The disk has a density less than of the fluid and floats in the fluid near the boundary surface. The disk is smooth, and has an index of refraction close to that of the fluid. The transparent rigid disk provides a flat surface which does not undulate and thus reduces the "sloshing effect."
The output signals of the orientation sensor are converted into digital data and presented to an interface. The interface converts the digital data into a format useable by a computer. For example, the data may be formatted by the interface to simulate a cursor control device, and presented to a computer as control signals for positioning a cursor on a display screen. Alternately, it may be desirable for the computer to react to gestures performed by a user. The interface or the computer may be configured to sample the orientation signals at regular intervals, store the signals, assemble the signals to form a time based sequence of orientations, and analyze the sequence to generate a gesture signal.
An object of the present invention is to provide a sourceless azimuthal sensor for monitoring the azimuthal orientation of a user.
Another object of the present invention is to provide a sourceless orientation sensor for detection of three independent orientation angles.
Another object of the present invention is to provide a sourceless gesture sensor.
Another object of the present invention is to provide an orientation sensor which determines its orientation relative to a planet's magnetic and gravitational fields.
Another object of the present invention is to provide an orientation sensor which operates over a wide range of tilt angles.
Another object of the present invention is to provide an orientation sensor which can operate when subject to rapid reorientations.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the claims.